U.S. patent application number 14/549625 was filed with the patent office on 2015-05-28 for inspection apparatus and inspection method.
This patent application is currently assigned to Lasertec Corporation. The applicant listed for this patent is Lasertec Corporation. Invention is credited to Kenshi ISHIWATARI, Hiroto NOZAWA, Ryoichiro SATOH, Kuniaki TAKEDA, Takamasa TSUBOUCHI.
Application Number | 20150144769 14/549625 |
Document ID | / |
Family ID | 53181815 |
Filed Date | 2015-05-28 |
United States Patent
Application |
20150144769 |
Kind Code |
A1 |
NOZAWA; Hiroto ; et
al. |
May 28, 2015 |
INSPECTION APPARATUS AND INSPECTION METHOD
Abstract
An inspection apparatus and an inspection method capable of
performing an inspection more accurately are provided. An
inspection apparatus according to the present invention includes a
light source 10 that illuminates a sample 30 in which a pattern is
formed, a detector 11 that detects light reflected from the sample
30 illuminated by the light source, and a processing device 50 that
performs an inspection based on a correlation between a brightness
value of a sample image obtained by the detector and a size in a
surface shape or a size in a width direction of the pattern of the
sample 30. The processing device 50 performs the inspection based
on a summation value obtained by adding up brightness values of
sample images with weights, the sample images being obtained under
a plurality of shooting conditions.
Inventors: |
NOZAWA; Hiroto; (Kanagawa,
JP) ; TAKEDA; Kuniaki; (Yokohama, JP) ;
ISHIWATARI; Kenshi; (Yokohama, JP) ; TSUBOUCHI;
Takamasa; (Yokohama, JP) ; SATOH; Ryoichiro;
(Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lasertec Corporation |
Yokohama |
|
JP |
|
|
Assignee: |
Lasertec Corporation
|
Family ID: |
53181815 |
Appl. No.: |
14/549625 |
Filed: |
November 21, 2014 |
Current U.S.
Class: |
250/208.1 |
Current CPC
Class: |
G06T 2207/30148
20130101; G01N 2021/95676 20130101; G06T 2207/10152 20130101; G01N
21/9501 20130101; G01N 2021/8848 20130101; G01N 2021/9513 20130101;
G01N 2021/8845 20130101; G06T 5/50 20130101; G06T 7/0004 20130101;
G01N 21/8851 20130101 |
Class at
Publication: |
250/208.1 |
International
Class: |
G01N 21/88 20060101
G01N021/88; G01N 21/95 20060101 G01N021/95 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 2013 |
JP |
2013243704 |
Claims
1. An inspection apparatus comprising: a light source that
illuminates a sample on which a pattern is formed; a detector that
detects light reflected from the sample illuminated by the light
source to take a sample image in which a position on a surface of
the sample is associated with a brightness value for each pixel;
and a processing device that performs an inspection based on a
correlation between the brightness value of the sample image
obtained by the detector and a size in a surface shape or a size in
a height direction of the pattern of the sample, wherein the
detector obtains a plurality of sample images by shooting the
sample under a plurality of shooting conditions, and the processing
device calculates a summation value obtained by adding up
brightness values of a plurality of sample images with weights for
each pixel or each area including a plurality of pixels, and
performs an inspection based on the calculated summation value for
each pixel or each area.
2. The inspection apparatus according to claim 1, wherein
parameters for the addition with weights are calculated based on a
measured value of the size obtained by measuring a reference sample
and a brightness value of a sample image of the reference sample by
using a statistical technique.
3. The inspection apparatus according to claim 2, wherein a
multiple regression analysis is used as the statistical
technique.
4. The inspection apparatus according to claim 1, wherein the
shooting condition is changed by changing at least one of a
wavelength of illumination light, polarization of the illumination
light, an illuminating angle of the illumination light, a shape of
the illumination light, a detecting angle of the detector, and an
angle of the sample.
5. The inspection apparatus according to claim 1, wherein when at
least one of the size in the surface shape and the size in the
height direction of the pattern is an item to be inspected,
shooting conditions whose sensitivities for an item other than the
item to be inspected are equivalent to each other are set.
6. The inspection apparatus according to claim 1, wherein the
sample is a semiconductor wafer, a TFT substrate, or a photomask,
and a CD of the pattern, a film thickness, a taper angle, or a
surface profile is inspected.
7. An inspection method comprising: illuminating a sample on which
a pattern is formed; detecting, by a detector, light reflected from
the illuminated sample to take a sample image in which a position
on a surface of the sample is associated with a brightness value
for each pixel; and performing an inspection based on a correlation
between the brightness value of the sample image obtained by the
detector and a size in a surface shape or a size in a height
direction of the pattern of the sample, wherein the detector
obtains a plurality of sample images by shooting the sample under a
plurality of shooting conditions, and a summation value obtained by
adding up brightness values of a plurality of sample images with
weights for each pixel or each area including a plurality of pixels
is calculated, and an inspection is performed based on the
calculated summation value for each pixel or each area.
8. The inspection method according to claim 7, wherein parameters
for the addition with weights are calculated based on a measured
value of the size obtained by measuring a reference sample and a
brightness value of a sample image of the reference sample by using
a statistical technique.
9. The inspection method according to claim 8, wherein a multiple
regression analysis is used as the statistical technique.
10. The inspection method according to claim 7, wherein the
shooting condition is changed by changing at least one of a
wavelength of illumination light, polarization of the illumination
light, an illuminating angle of the illumination light, a shape of
the illumination light, a detecting angle of the detector, and an
angle of the sample.
11. The inspection method according to claim 1, wherein when at
least one of the size in the surface shape and the size in the
height direction of the pattern is an item to be inspected,
shooting conditions whose sensitivities for an item other than the
item to be inspected are equivalent to each other are set.
12. The inspection method according to claim 1, wherein the sample
is a semiconductor wafer, a TFT substrate, or a photomask, and a CD
of the pattern, a film thickness, a taper angle, or a surface
profile is inspected.
Description
INCORPORATION BY REFERENCE
[0001] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2013-243704, filed on
Nov. 26, 2013, the disclosure of which is incorporated herein in
its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an inspection apparatus and
an inspection method.
[0004] 2. Description of Related Art
[0005] As a technique for swiftly inspecting a surface of a
semiconductor wafer or the like, a macro inspection apparatus has
been used (Non-patent literature 1 and 2). Since a macro inspection
apparatus takes an image of a wafer at a low magnification, it can
inspect the whole wafer in a short time. For example, the macro
inspection apparatus disclosed in Non-patent literature 1 takes an
image of a wafer by illuminating the wafer in an oblique direction.
The intensity of the reflected light changes as the line width of a
pattern (line width) changes. Therefore, linearity between line
widths and brightness values is obtained in Non-patent literature
1.
[Non-Patent Literature 1] An In-line Image Quality Monitoring
System for Imaging Device Fabrication using Automated
Macro-Inspection, Tohru Sasaki et al., Proc. SPIE 6152, Metrology,
Inspection, and Process Control for Microlithography XX, 61522W
(Mar. 24, 2006) [Non-Patent Literature 2] Full wafer macro-CD
imaging for excursion control of fast pattering process, Lars
Markwort et al., Proc. SPIE 7638, Metrology, Inspection, and
Process Control for Microlithography XXIV, 763807 (Apr. 1,
2010)
[0006] In a macro inspection apparatus, an inspection is performed
by associating intensities of received light (brightness values) of
a detector with CD values. For example, in FIG. 1 of Non-patent
literature 1, the brightness value increases as the pattern width
becomes wider. In other words, a brightness distribution
corresponds to a CD distribution, thus making it possible to
perform a CD inspection based on the brightness distribution.
[0007] Regarding the above-described inspection apparatus, it is
desired to perform an inspection more accurately. However, the
brightness value in the detector changes depending on the pattern
and the film-thickness of a base layer and the like as well as
depending on the CD value. That is, the brightness value includes
information of the film-thickness and the like in addition to the
CD value. Further, it also includes changes of the brightness value
caused by shading and the like of the optical system. As a result,
in Non-patent literature 1, there is a possibility of occurrences
of an error due to the association between the CD values and the
brightness values could increase. Consequently, there is a problem
that it is very difficult to accurately perform an inspection in
the above-described method.
[0008] The present invention has been made in view of the
above-described circumstances, and an object thereof is to provide
an inspection apparatus and an inspection method capable of
performing an inspection more accurately.
SUMMARY OF THE INVENTION
[0009] A first exemplary aspect of the present invention is an
inspection apparatus including: a light source that illuminates a
sample on which a pattern is formed; a detector that detects light
reflected from the sample illuminated by the light source; and a
processing device that performs an inspection based on a
correlation between a brightness value of a sample image obtained
by the detector and a size in a surface shape or a size in a height
direction of the pattern of the sample, in which the processing
device performs the inspection based on a summation value obtained
by adding up brightness values of sample images with weights, the
sample images being obtained under a plurality of shooting
conditions. This configuration makes it possible to perform an
accurate inspection.
[0010] In the above-described inspection apparatus, parameters for
the addition with weights may be calculated based on a measured
value of the size obtained by measuring a reference sample and a
brightness value of a sample image of the reference sample by using
a statistical technique. This makes it possible to use appropriate
parameters and thereby to perform an inspection more
accurately.
[0011] In the above-described inspection apparatus, a multiple
regression analysis may be used as the statistical technique. This
makes it possible to use parameters that reduce an error and
thereby to perform a highly accurate inspection.
[0012] In the above-described inspection apparatus, the shooting
condition may be changed by changing at least one of a wavelength
of illumination light, polarization of the illumination light, an
illuminating angle of the illumination light, a shape of the
illumination light, a detecting angle of the detector, and an angle
of the sample. This makes it possible to easily set appropriate
shooting conditions.
[0013] In the above-described inspection apparatus, when at least
one of a size of the surface shape and a size in the height
direction of the pattern is an item to be inspected, shooting
conditions whose sensitivities for an item other than the item to
be inspected are equivalent to each other are preferably set. This
makes it possible to appropriately extract information of the item
to be inspected and thereby to perform an inspection with the
appropriate information.
[0014] In the above-described inspection apparatus, the sample may
be a semiconductor wafer, a TFT substrate, or a photomask, and a CD
of the pattern, a film thickness, a taper angle, or a surface
profile may be inspected. This makes it possible to accurately
inspect the CD value of the pattern, the film thickness, the taper
angle, or the surface profile.
[0015] Another exemplary aspect of the present invention is an
inspection method including: illuminating a sample on which a
pattern is formed; detecting light reflected from the sample
illuminated; and performing an inspection based on a correlation
between a brightness value of a sample image obtained and a size in
a surface shape or a size in a height direction of the pattern of
the sample, in which the inspection is performed based on a
summation value obtained by adding up brightness values of sample
images with weights, the sample images being obtained under a
plurality of shooting conditions.
[0016] In the above-described inspection method, parameters of the
addition with weights may be calculated based on a measured value
of the size obtained by measuring a reference sample and a
brightness value of a sample image of the reference sample by using
a statistical technique. This makes it possible to use appropriate
parameters and thereby to perform an inspection more
accurately.
[0017] In the above-described inspection method, a multiple
regression analysis may be used as the statistical technique. This
makes it possible to use parameters that reduce an error and
thereby to perform a highly accurate inspection.
[0018] In the above-described inspection method, the shooting
condition may be changed by changing at least one of a wavelength
of illumination light, polarization of the illumination light, an
illuminating angle of the illumination light, a shape of the
illumination light, a detecting angle of the detector, and an angle
of the sample. This makes it possible to easily set an appropriate
shooting condition.
[0019] In the above-described inspection method, when at least one
of a size of the surface shape and a size in the height direction
of the pattern is chosen as an item to be inspected, shooting
conditions whose sensitivities for an item other than the item to
be inspected are substantially equal to each other are preferably
set. This makes it possible to appropriately extract information of
the item to be inspected and thereby to perform an inspection with
the appropriate information.
[0020] In the above-described inspection method, the sample may be
a semiconductor wafer, a TFT substrate, or a photomask, and a CD
value of the pattern, a film thickness, a taper angle, or a surface
profile may be inspected. This makes it possible to accurately
inspect the CD value of the pattern, the film thickness, the taper
angle, or the surface profile.
[0021] According to the present invention, an inspection apparatus
and an inspection method capable of performing an inspection more
accurately can be provided.
[0022] The above and other objects, features and advantages of the
present invention will become more fully understood from the
detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not to be considered as limiting the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows an overall configuration of an inspection
apparatus according to an exemplary embodiment;
[0024] FIG. 2 is a block diagram showing a configuration of a
processing device;
[0025] FIG. 3 schematically shows a semiconductor wafer, which is a
reference sample; and
[0026] FIG. 4 shows a correlation between measured CD values and
summation values of brightness values.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0027] Exemplary embodiments according to the present invention are
explained hereinafter with reference to the drawings. The following
explanations are given just to show preferred exemplary embodiments
according to the present invention, and the scope of the present
invention should not be limited to the below-shown exemplary
embodiments. In the following explanations, components/structures
to which the same symbols are assigned are substantially equivalent
to each other.
[0028] An inspection apparatus according to this exemplary
embodiment is a macro inspection apparatus that inspects a sample
such as a semiconductor wafer on which a fine pattern is formed.
The inspection apparatus performs a macro inspection based on
brightness values of sample images. For example, the inspection
apparatus inspects a pattern that is formed by liquid immersion
exposure, EUV (Extreme Ultra Violet) exposure, or the like. The
sample may be a semiconductor wafer for a NAND-type flash memory, a
DRAM (Dynamic Random Access Memory), an SRAM (Static Random Access
Memory), or the like, on which a periodic pattern is formed. The
inspection apparatus takes images of the sample on which a pattern
is periodically formed, and detects a line width (CD) distribution
of the pattern, a film-thickness distribution, a taper angle
distribution, and/or a surface profile. Alternatively, the
inspection apparatus may inspect a patterned substrate for a liquid
crystal display panel such as a TFT (Thin film transistor)
substrate, or a photomask instead of the semiconductor wafer. As an
example, a case where a semiconductor wafer is inspected is
explained hereinafter.
[0029] A configuration of an inspection apparatus according to this
exemplary embodiment is explained with reference to FIG. 1. FIG. 1
is a perspective view showing an overall configuration of the
inspection apparatus. The inspection apparatus includes a light
source 10, a detector 11, a stage 30, and a processing device 50.
Further, FIG. 1 shows a three-dimensional orthogonal coordinate
system consisting of XYZ-axes for clarifying the explanation. Note
that the Z-direction is the vertical direction, and is a direction
perpendicular to the pattern formation surface of a sample 20. The
X- and Y-directions are horizontal directions, and are directions
in parallel with the pattern formation surface of the sample
20.
[0030] The light source 10 and the detector 11 are disposed above
the sample 20. The light source 10 is, for example, a linear light
source that emits illumination light having a linear shape.
Alternatively, the light source 10 may emit illumination light
having a ring shape or a planar shape. The light source 10 emits,
for example, illumination light such as visible light or infrared
light. The light source 10 illuminates the sample 20 in an oblique
direction, i.e., in a direction inclined from the Z-axis.
Alternatively, the light source 10 illuminates the sample 20 from a
position located on the Z-axis. The illumination light uniformly
illuminates a linear shape area along the Y-direction on the
surface of the sample 20. On the surface of the sample 20, the
length of the illumination light along the Y-direction extends over
the entire inspection area of the sample 20.
[0031] The illumination light emitted from the light source 10
illuminates a linear shape area on the surface of the sample 20.
Then, light reflected in the illuminated linear shape area is
detected by the detector 11. The detector 11 may be a line sensor
camera in which light-receiving pixels are arranged in a row in the
Y-direction. Therefore, since the intensity of the reflected light
changes according to the surface state of the sample 20, the
pattern size, and the like, the brightness value in the detector 11
changes.
[0032] The pixel size of the detector 11 is, for example, in the
order of several .mu.m to several tens of .mu.m. Further, the pixel
size on the sample 20 is roughly the same as that of the detector
11. Note that a line sensor in which photodiodes are arranged in a
row can be used as the detector 11. The detector 11 and the light
source 10 are obliquely disposed with respect to the Z-direction.
The pattern size on the sample 20 is sufficiently smaller than the
pixel size on the sample 20. Note that the illuminating angle of
the illumination light emitted from the light source 10 on the
XZ-plane may be equal to the angle of the detector 11, or may be
different from the angle of the detector 11.
[0033] Further, the respective angles of the light source 10 and
the detector 11 are changeable. For example, the illuminating angle
of the illumination light can be changed by rotating the light
source 10 around the Y-axis. Further, the detecting angle of
detector 11 can be changed by rotating the detector 11 around the
Y-axis. The respective angles of the light source 10 and the
detector 11 can be adjusted independently of each other.
Alternatively, the respective angles of the illumination light and
the detector 11 may be changed by tilting the stage 30 around the
X- or Y-axis.
[0034] The sample 20, which is the object to be inspected, is
placed on the stage 30. The sample 20 is a patterned substrate such
as a mask or a semiconductor wafer. The surface of the sample 20 is
perpendicular to the Z-direction. Further, the stage 30 can be
moved in the X-direction. The detector 11 detects light reflected
in the area illuminated by the light source 10 while the stage 30
is being moved in the X-direction. Then, detection data according
to the brightness of the light detected by the detector 11 is input
to the processing device 50. Further, the processing device 50
controls the driving of the stage 30. Then, the processing device
50 visualizes the brightness changes of the light detected by the
detector 11. In this way, a reflection image of the entire surface
of the sample 20 can be obtained.
[0035] Further, the stage 30 can rotate around the Z-axis. By doing
so, the angle of the sample 20 on the XY-plane can be changed. That
is, the angle of the pattern with respect to the illumination light
can be changed.
[0036] The light source 10 simultaneously illuminates the entire
length of the sample 20 in the Y-direction. That is, an optical
system having a low magnification and a wide field of vision is
used. In this way, since an inspection can be performed with a high
throughput by using an optical system having a low magnification,
the inspection can be performed at a speed of 10 to 150 samples per
hour. Since the throughput is high, every wafer can be inspected
during the manufacturing process.
[0037] For example, the processing device 50 obtains images of a
semiconductor wafer on which a pattern of a resist, lines, or the
like is formed. The processing device 50 performs an inspection
based on the obtained images. For example, when there are
variations in the film-thickness or in the CD, the intensity of the
reflected light changes. Consequently, the brightness of the sample
images changes. Therefore, it is possible to inspect the variations
in the film-thickness, in the CD, or the like based on the
brightness changes of the sample images. An example case where
variations in the CD are inspected is explained hereinafter.
[0038] In the following example, the processing device 50 is, for
example, an information processing apparatus such as a personal
computer, and performs processes for obtained sample images. The
processing device 50 performs an inspection based on a correlation
between the brightness values of sample images obtained by the
detector 11 and the sizes of the pattern in the height direction or
in the width direction of the sample 20. Specifically, the
processing device 50 performs processes for carrying out a CD
inspection. When an abnormality in the CD is detected by the CD
inspection, the detection result is fed back to the manufacturing
process and the like and a rework process or the like is performed
based on the feedback. As a result, the productivity can be
improved.
[0039] In order to perform a CD inspection, the detector 11 takes
images of the sample 20 under different shooting conditions. That
is, the inspection apparatus obtains sample images while changing
the shooting condition. Then, in this exemplary embodiment, the
processing device 50 converts brightness values of a plurality of
sample images into a CD value(s). The processing device 50 inspects
the sample 20 based on the plurality of sample images that are
obtained under different shooting conditions.
[0040] A configuration of the processing device 50 and processes
performed thereby are explained with reference to FIG. 2. FIG. 2 is
a block diagram showing a configuration of the processing device
50. The processing device 50 includes a first storage unit 51, a
second storage unit 52, a parameter calculation unit 53, a
parameter storage unit 54, and a determination unit 55.
[0041] The processing device 50 is a personal computer or the like
and executes the following process. The units of the processing
device 50 may each be configured, as hardware, by a CPU, memory, or
a circuit in another form, or, as software, by a program loaded
into a memory. Accordingly, these function blocks may be realized
in a form of hardware, software, or a combination of the two as
commonly understood by persons having ordinary skill in the art,
and are not be limited to any specific form. Further, it is to be
noted that the elements having substantially the same features
depicted in the drawings will be assigned the same reference
numerals, and the description thereof will not be repeated as
appropriate.
[0042] Further, the program may be stored by using various types of
non-transitory computer readable medium, and supplied to computers.
The non-transitory computer readable medium includes various types
of tangible storage medium. Examples of the non-transitory computer
readable medium include a magnetic recording medium (such as a
flexible disk, a magnetic tape, and a hard disk drive), a
magneto-optic recording medium (such as a magneto-optic disk), a
CD-ROM (Read Only Memory), a CD-R, and a CD-R/W, and a
semiconductor memory (such as a mask ROM, a PROM (Programmable
ROM), an EPROM (Erasable PROM), a flash ROM, and a RAM (Random
Access Memory)). Further, the program may be supplied to computers
by using various types of transitory computer readable media.
Examples of the transitory computer readable media include an
electrical signal, an optical signal, and an electromagnetic wave.
The transitory computer readable media may be used to supply
programs to computer through a wire communication path such as an
electrical wire and an optical fiber, or wireless communication
path.
[0043] As explained above, the inspection apparatus obtains sample
images while changing the shooting condition. The first storage
unit 51 stores image data detected by the detector 11. That is, the
first storage unit 51 stores the brightness value of each pixel of
the detector 11. The second storage unit 52 stores image data
detected by the detector 11. That is, the second storage unit 52
stores the brightness value of each pixel of the detector 11. The
sample image stored in the first storage unit 51 and that stored in
the second storage unit 52 are taken under mutually different
shooting conditions. In the following explanation, the sample image
stored in the first storage unit 51 is referred to as "first sample
image" and the sample image stored in the second storage unit 52 is
referred to as "second sample image". That is, the sample image
taken under a first shooting condition becomes the first sample
image and the sample image taken under a second shooting condition
becomes the second sample image.
[0044] Examples of the shooting conditions include the angle of the
illumination light around the Y-axis, the angle of the detector 11
around the Y-axis, the angle of the sample 20 around the Z-axis,
the wavelength of the illumination light, the polarization of the
illumination light, and the spot shape of the illumination light on
the sample 20. A plurality of sample images are obtained while
changing at least one of the angle of the illumination light around
the Y-axis, the angle of the detector 11 around the Y-axis, the
angle of the sample 20 around the Z-axis, the wavelength of the
illumination light, the polarization of the illumination light, and
the spot shape of the illumination light. By doing so, appropriate
shooting conditions can be easily selected.
[0045] When the angle of the illumination light around the Y-axis
is changed, the light source 10 may be moved. When the angle of the
detector 11 around the Y-axis is changed, the detector 11 may be
moved. Alternatively, the stage 30 may be tilted in the
Y-direction. When the angle of the sample 20 around the Z-axis is
changed, the stage 30 may be rotated. Alternatively, the direction
in which the sample 20 is placed on the stage 30 may be changed.
When the wavelength of the illumination light is changed, a
wavelength filter may be placed on the optical path. Then, the
wavelength of the illumination light can be changed by changing the
wavelength filter placed on the optical path. Alternatively, the
wavelength of the illumination light may be changed by using a
plurality of different light sources.
[0046] When the polarization state is changed, a polarizing plate
may be placed on the optical path. For example, the polarization
direction can be changed by rotating the polarizing plate by 90
degrees. When the spot shape of the illumination light is changed,
the width of the line illumination, for example, may be changed.
Alternatively, ring illumination may be used. When the ring
illumination is used, the shooting condition may be changed by
changing the size of the ring illumination. In this way, the
shooting condition is changed so that the intensity of the light
reflected on the sample 20 changes. Needless to say, the first and
second sample images may be obtained while changing at least two of
the above-listed shooting conditions at the same time.
[0047] The parameter calculation unit 53 calculates parameters for
an addition with weights. A calculation method for the parameters
for the addition with weights will be explained later. The
parameter storage unit 54 stores the parameters calculated by the
parameter calculation unit 53. The determination unit 55 performs
an addition of the first and second sample images with weights
using the parameters and thereby generates a summation image. In
particular, the determination unit 55 calculates a summation value
obtained by adding up brightness values with weights for each
pixel. Since the position of the stage 30 is controlled by the
processing device 50, a brightness value according to the
XY-position on the sample 20 is detected. Alternatively, instead of
adding up brightness values for each pixel, brightness values for
each specified area may be added up. For example, average values of
brightness values over a plurality of pixels may be added up with
weights.
[0048] The determination unit 55 converts brightness values into a
CD value(s) by adding up a plurality of sample images with weights.
The determination unit 55 performs a pass/fail determination by
comparing the brightness value of the summation image with a
threshold. For example, the determination unit 55 determines
whether or not the summation value of brightness values is within a
normal range between upper and lower limit values. When the
brightness value of the summation image is between the upper and
lower limit values, the determination unit 55 determines that it is
normal. On the other hand, when the brightness value of the
summation image is higher the upper limit value or lower than lower
limit value, the determination unit 55 determines that it is
abnormal.
[0049] For example, brightness values are converted into a CD
value(s) by performing an addition with weights in accordance with
the below-shown Expression (1).
CD value=Image1.times.a1+Image2.times.a2+b (1)
[0050] In the expression, Image1 is a brightness value of a first
sample image and Image2 is a brightness value of a second sample
image. Constants a1, a2 and b are parameters for an addition with
weights. It is possible to associate brightness values of a
plurality of sample images with a CD value(s) by using the
parameters for the addition with weights.
[0051] The brightness value changes according to the CD value of
the pattern on the sample 20. Similarly, the brightness value
changes according to the film-thickness of the pattern on the
sample 20. Therefore, the brightness value distribution of a sample
image includes information about the CD distribution and the
film-thickness distribution. That is, since the brightness value
depends on the CD value and the film-thickness, the change of the
brightness value due to the film-thickness change is added to the
change of the brightness value due to the CD change. Further, the
change of the brightness value due to shading and the like of the
optical system is also added. Therefore, in the configuration in
which the brightness value of only one sample image is compared
with a threshold, when there is a brightness change, it is
impossible or very difficult to determine whether the change is
caused by variations in the CD, variations in the film-thickness,
or shading of the optical system. As described above, in the
related art method, it is very difficult to obtain information
about only the item to be inspected.
[0052] Accordingly, this exemplary embodiment uses a plurality of
sample images obtained under mutually different shooting
conditions. For example, a plurality of shooting conditions having
different sensitivities to the item to be inspected and the same
sensitivity to an item(s) other than the item to be inspected are
selected. That is, when the CD value is the item to be inspected,
shooting conditions having different sensitivities to the CD value
and the same sensitivity to the film-thickness and the like, i.e.,
an item(s) other than the item to be inspected (i.e., the CD value)
are selected. As a result, it is possible to extract information
about only the item to be inspected by performing an addition with
weights for the selected plurality of shooting conditions. In this
way, it is possible to associate the summation value with the CD
value with high accuracy. Therefore, the CD inspection can be
performed more accurately.
[0053] As an example of the above-described inspection procedure,
the determination of the weighting parameters is made only when the
inspection recipe is created. Then, the inspection time can be
reduced by applying the above-described determined weighting
parameters during the inspection that is performed after the
inspection recipe is created.
[0054] Further, as described above, the shooting conditions such as
the angle of the illumination light around the Y-axis, the angle of
the detector 11 around the Y-axis, the angle of the sample 20
around the Z-axis, the wavelength of the illumination light, the
polarization of the illumination light, and the spot shape of the
illumination light are changed. In this way, appropriate shooting
conditions can be easily set.
[0055] For the parameter calculation performed by the parameter
calculation unit 53, a statistical technique can be used. For
example, as shown in FIG. 3, a reference sample 21 whose CD value
changes according to the position in the X-direction is prepared.
In the case of the reference sample 21 shown in FIG. 3, the CD
value increases as the X-coordinate increases. Sample images of the
reference sample 21 having such characteristics are obtained while
changing the shooting condition. That is, a first reference sample
image is taken under a first shooting condition and a second
reference sample image is taken under a second shooting
condition.
[0056] In addition to the acquisition of the reference sample
images, the CD value of the reference sample is measured by using a
measuring device different from the inspection apparatus. In this
example, an actual CD value(s) is measured by CD-SEM (Scanning
Electron Microscopy). Alternatively, an actual CD value(s) may be
measured by OCD (Optical Critical Dimension) measurement. Then, a
correlation between measured CD values and brightness values is
obtained. For example, the parameter calculation unit 53 uses a
multiple regression analysis as a statistical technique and thereby
calculates the parameters (a1, a2 and b). The parameter calculation
unit 53 performs a multiple regression analysis in which the
brightness values of the first and second reference sample images
are used as independent variables and the CD value is used as a
dependent variable. By doing so, parameters (a1, a2 and b) that
reduce the error can be calculated. In this way, the correlation
between the CD values and the summation values can be obtained. The
correlation between the measured CD values and the summation values
is linear as shown in FIG. 4. Alternatively, the weighting
variables may be set so that a curved distribution such as a
quadratic function is obtained when the weighting function is
obtained. In FIG. 4, the horizontal axis represents measured CD
values and the vertical axis represents summation values.
[0057] Then, the parameter storage unit 54 stores the parameters
(a1, a2 and b) calculated by the parameter calculation unit 53.
Then, images of a sample 20, which is the object to be inspected,
are taken under the same shooting conditions as those used when the
parameters are determined. The inspection apparatus obtains a first
sample image under the first shooting condition and a second sample
image under the second shooting condition. Then, the brightness
values of the first and second sample images are added up with
weights by using the parameters (a1, a2 and b) in accordance with
the above-shown Expression (1). In this way, the brightness values
of the sample images can be converted into a CD value(s).
[0058] As described above, weighting parameters are calculated by
using a statistical technique. That is, the parameters are
calculated so that the error between the summation value obtained
by the addition of the reference sample images with weights and the
measured CD value is minimized. In this way, appropriate parameters
can be set. Therefore, an inspection can be performed more
accurately. Note that the measurement of the CD value may be
performed by using a measuring device other than the CD-SEM.
Alternatively, a reference sample whose CD value(s) is already
known may be used.
[0059] In the above explanation, the sample images are obtained
under the first and second shooting conditions. However, sample
images may be obtained under three or more different shooting
conditions. That is, brightness values of three or more sample
images may be added up with weights. Even in this case, parameters
can be set by a statistical technique using brightness values of
reference sample images in a similar manner to that for the
above-described example. Note that the number of weighting
parameters increases according to the number of shooting
conditions. For example, optimal weighting parameters can be
calculated by performing a multiple regression analysis in which
brightness values of reference sample images are used as
independent variables. Then, the brightness values of the sample
images are converted into a CD value(s) by using the calculated
weighting parameters. By increasing the number of shooting
conditions as described above, an inspection could be performed
more accurately.
[0060] Further, reference sample images may be taken under three or
more shooting conditions. Then, only some of these reference sample
images may be used when parameters are set. For example, reference
sample images may be obtained under three different shooting
conditions, and then two of the three shooting conditions with
which the error decreases may be selected. The inspection time can
be reduced by reducing the number of shooting conditions. As a
result, the throughput can be increased.
[0061] The above-described inspection method makes it possible to
inspect a CD distribution with an accuracy of 1 nm or smaller. Note
that although a CD (Critical Dimension) inspection is explained in
the above-described examples, a film-thickness inspection can also
be performed in a similar manner. Further, a taper angle inspection
and a surface profile inspection can also be performed in a similar
manner. For example, in the case of the film-thickness inspection,
for the film-thickness, weighting parameters are set by using
reference sample images taken under different shooting conditions
as in the case of the CD value. The weighting parameters in the
film-thickness inspection have values different from those of the
weighting parameters in the CD inspection. Then, brightness values
of sample images are added up with weights and an abnormality in
the film-thickness can be determined based on the summation value.
Further, the film-thickness inspection may use shooting conditions
different from those for the CD inspection. In this way, the
brightness values are converted to film-thicknesses by calculating
the summation value of brightness values using the weighting
parameters. As a result, the film-thickness can be accurately
inspected. Further, different weighting parameters can be set for
each of the CD, the film thickness, the taper angle, and the
surface profile which are the size in the surface shape or the size
in the height direction of a pattern. When at least one of the size
in the surface shape or the size in the height direction of a
pattern is the item to be inspected, shooting conditions having
equivalent sensitivities for an item(s) other than the item to be
inspected may be set.
[0062] In the above explanation, the present invention is applied
to a CD inspection and a film-thickness inspection of a
semiconductor wafer. However, inspections to which the present
invention can be applied are not limited to these inspections. That
is, an inspection to which the present invention is applied can be
performed for any patterned substrates on which a pattern that is
finer than the light-receiving pixels on the sample is formed. For
example, the present invention can be applied to an inspection of a
patterned substrate for a display panel such as a TFT substrate and
an inspection of a photomask substrate. Further, in this exemplary
embodiment, an inspection can be performed based on a correlation
between brightness values of sample images and the size of the
surface shape or the size in the height direction of a pattern of
the sample. As a result, inspections of the surface shape of a
pattern, surface roughness, a pattern width, a pattern interval, a
taper angle, height information, a surface profile, and so on can
be performed. Further, since images of a sample are taken at a low
magnification, the whole sample can be inspected in a short
time.
[0063] From the invention thus described, it will be obvious that
the embodiments of the invention may be varied in many ways. Such
variations are not to be regarded as a departure from the spirit
and scope of the invention, and all such modifications as would be
obvious to one skilled in the art are intended for inclusion within
the scope of the following claims.
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